$g(x) = -3x-8$ $g\Big($
Answer: We need to solve an equation with the function's formula $-3x-8$ on one side and the given output $10$ on the other side. $\begin{aligned} -3x-8&=10\\\\ -18&=3x\\\\ -6&=x\end{aligned}$ Therefore, $g(-6)=10$. The answer $x=-6$